During the past year, the VRC's Vector Core created and tested new vaccine vectors expressing different HIV proteins, including novel forms of envelope proteins. In addition,different methods and routes of administration as well as prime/boost combinations were tested to further optimize HIV vaccine strategies. DNA, VLP, nanoparticles and other vectors were tested. Several candidate vaccines elicited promising immunogenicity data in preliminary studies and are being tested further. Specific accomplishments include: Different prime boost vectors encoding HIV-1 Env including DNA and proteins were compared to previously developed delivery systems. T cell immunogenicity was assessed by intracellular cytokine staining or by analyzing tetramer positive cells. Studies to optimize the CD4-binding site (CD4bs) as a basis for vaccine development were continued. The HIV Outer domain (OD) of gp120 envelope is a minimal unit containing the CD4bs which is targeted by broadly neutralizing antibodies, VRC01 and b12, therefore thought to be an attractive immunogen to induce such antibodies. During the past year studies continued to engineer the OD and other epitopes on the CD4bs to optimize their use as immunogens. In addition, ferritin nanoparticles experssing HIV envelope were analyzed to induce CD4bs antibodies, identified by newly developed assays based on the resurfaced stabilized gp120 core with antigenic specificity for the initial site of CD4 attachment of gp120. Epitopes recognized by vectors expressing neutralizing antibodies were also analyzed and tested for their ability to induce similar types of antibodies, in vivo.